The present invention relates to plastic containers and in particularly to plastic containers which have a reinforcing ring in the base to strengthen the base against undesirable deformation.
In recent years, the use of plastic containers for beverages, and particularly carbonated beverages has increased dramatically. These containers are typically blow molded from an injection molded polyethylene terephthalate (PET) preform. A difficulty, however, with use of plastic containers for carbonated beverages is in providing sufficient strength in the container base to resist deformation. The internal pressure in a container filled with a carbonated beverage can range from approximately 60 psig at room temperature to as high as 100 psig at 100.degree. F. These pressures can produce deformation in a plastic container at its base which can result in a container no longer having a flat bottom surface perpendicular to the upright axis of the bottle such that the bottle will no longer stand upright on a horizontal supporting surface. In addition to the stability problem of a bottle with a deformed base, when the base is deformed, the volume of the bottle typically increases. The volume increase results in a lowering of the liquid fill line such that consumers may be lead to believe that the bottle was not properly filled or sealed.
One solution to the problem of base deformation is to mold the bottle with a hemispherically shaped base extending downwardly from the sidewall of the container. The hemispherical shape, although resistant to deformation, requires a separate support stand to enable the container to stand upright. Typically, a second plastic piece, often referred to as a base cup, is glued to the hemispherical bottom of the bottle. The base cup includes a bottom wall defining a flat horizontal surface and a generally cylindrical wall extending upwardly from the bottom wall and engaging the side of the plastic bottle.
A major disadvantage with a base cup container is the additional material cost required for the base cup. Base cups are often molded of polyethylene which has dramatically increased in price. The polyethylene base cup contributes almost half of the container material cost while providing approximately one-third of the container material weight. Another difficulty with the use of PET bottles and polyethylene base cups is in recycling the plastic material of the container. Before the plastic can be recycled, the PET bottle must be separated from the polyethylene base cup.
Accordingly it is an object of this invention to provide a container which is more economical to produce than a typical base cup container in terms of both the cost of material and the quantity of material required.
It is a further object of the invention to provide a container constructed entirely of a single plastic material such that separation of the different plastic materials is not necessary before recycling the container.
The plastic container of this invention includes a blow-molded plastic bottle having a generally cylindrical sidewall with a base structure at its lower end. The base structure includes a bottom wall extending downwardly from the lower end of the sidewall. The center portion of the bottom wall is inverted upwardly into the container forming a dome in the center of the base. A base having this type of central dome is often referred to as a champagne bottle base.
A plastic reinforcing ring is attached to the bottom wall around the outer side of the bottle adjacent the lower end of the bottle. The plastic ring is positioned on the outer side of the bottle such that the carbonation pressure within the bottle exerts a downward force on the central dome which creates tension in the ring. This tension maintains the ring in a position on the base structure in which the ring reinforces the base structure to prevent the central dome from everting.
The reinforcing ring can be injection molded of the same plastic material used to blow-mold the bottle such that separation of the ring from the bottle is not necessary before recycling the material in the container. Alternatively, the ring can also be made of a lightweight metal such as aluminum.
The container can be manfactured by inserting the ring into the base portion of a blow-mold and blow-molding the bottle within the ring. By molding the bottle with the ring in this manner, an assembly process step to attach the ring to the base structure is not required. The manufacturing process of the container of this invention is thus simplified over that used for manufacturing a base cup container.
The reinforcing ring can be configured such that it extends downwardly below the lowermost portion of the bottle to form a lowermost planar surface for supporting the container upright on a horizontal surface.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.